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A. E. LUNDE-LL AND A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM.

APPLICAHON FILED MAY 28, ms

0 s 04!- T m m p MS n15 f wn VMB MM m 5 m Z a e/ P Mr 4AM A. E. LUNDELLAND A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAY 25, IBM].

Patented Mar. 23, 1920.

4 SHEETS-SHEET 2- A. E.'LUNDELL AND A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM. APPLICAUON HLED M128. 1918.

1,334,308. Patented Mag 23, 1920.

4 SHEETS-SHEET 3.

4/w1 A and? Ar/hur 5. 5,0010- A. E. LUNDELL AND A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM.

APPLHZATIDN FILED MAY 28. I918.

Patented Mar. 23, 1920.

4 SHEETS-SHEET 4...

/n wnfors Alba/4 A". Law

UNITED STATES PATENT OFFICE.

ALDEN E. LUNDELL AND ARTHUR B. SPERRY, OF NEW YORK, N. Y., ASSIGNORS TOWESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A COR,-

POBATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Mar. 23, 1920.

description.

This invention relates to telephone exchange systems in which automaticswitch ing is employed in extending and coluplet ing connections.

ore particularly it relates to a telephdne system involving a pluralityof private branch exchanges, arranged to serve sub scribers lines ofboth the manual and automatic types, and rovided with a novel-system oftrunk ci&uits interconnecting the several exchangesin such manner thatsubscribers belonging to one exchange may readily extend connections toother exchanges, and thence obtain communication with subscribers Whoselines terminate therein.

An object of the invention consists gen orally. in the provision oftrunk circuits, in a system of this character, by means of which asubscriber at oneexchange may extend his line over a trunk to a secondexchange, and by the agency of selective switching apparatus extend theconnection to a trunk outgoing from the second exchange to a thirdexchange, and finally by the operation of connection. to a desired linebelonging to such third exchange.

A feature of the present invention con sists in the provision of meanswhereby a connection incoming to a second exchange overan inter exchangetrunk circuitfrom a subscribers line at a first exchange may be furtherextended, by a selective switch, either to other switches having accessto lines indi' vidual to said second exchange, or to a second interexchange trunk outgoing from the second exchange and terminating in aswitch at a third exchange.

Another feature relates to means which is incidentally renderedeffective, upon twp inter exchange trunks being thus connected in tandematan intermediate exchange, to

automatically convert said trunks into a single through trunk circuitsuitable for the transmission of switch operating impulses directly fromthe calling to the called exchange, without the intervention of anyrepeatmg medium at the intermediate exchange.

Still another fcature consists in )roviding a through trunk circuit froma ca ling to a called exchange, comprising two inter exchange trunksconnected in tandem as above described, which remains in a non-ta1kingcondition during 0%: switch operatin period. Upon the response of thecall subscriber means are operated to transform said through trunkcircuit from a condition adapted to the transmission of impulses to acondition suitable for the transmissionof conversational currents.

A further feature resides in the provision of means whereby an operatorat a calling exchange is given supervision of 9. called line in a.distant exchange over said through trunk circuit.

Other and further features will become apparent from a consideration ofthe following description and the appended claims.

In the drawingaFigures 1, 2, 3 and 4,

when arranged consecutively in the order named, disclose so much of atelephone system as is necessary to a comprchensivefln derstanding ofthe present invention. Fig. 1 shows a portion of a telephone exchangewith a manual suhscribers line terminating in an operators posit'on, andan automatic suhscribers line teri inating. in automatic switchestheiein. There is also shown the outgoing end of an inter exchange trunkter' minating in a jack at said operators position, and in multiples ofl the automatic switches; Fig. .2 shows. a portion of the equipment at asecond exchange illustrating a selector switch-in which the incoming endof said interexchangc trunk terminates; Fig. 3 shows a second interexchange trunk i outgoing from the second exchange and ter- Adescription will now be given of the operation of the system involvingthe features of invention.

Assume first that a subscriber provided with a manual substation, as thesubstation 100 at the first exchange desires to converse with asubscriber whose line terminates at the second exchange, as the line300, 301. Upon removing his receiver to initiate the call, his line isassociated in any well-known manner with an operatofis position at theexchange. The oierator on learnin that the wanted line belongs toanother exdhange inserts the plug 101 of her cord circuit 102 into thejack 103 of an idle outgoing trunk circuit 104, 105 leading to suchexchange. By the insertion of the plug in the jack a circuit is closedfrom ground, winding of relay 106, sleeve of the plug and sleeve of thejack, winding of relay 107, to battery. Relay 107 energizes and at itsright-hand armature closes a circuit to display the supervisory lamp108. At its left-hand armature, relay 107 applies a ground to the. testterminal 109 at a selector switch 110, 111. 112 to render trunk 101,105i busy to said selector in case a subscriber at an automaticsubstation, as the substation 113, attempts to extend a call to thesecond ex change over this trunk circuit. The stepping relay 114 isenergized at this time over a circuit from battery, contact 115 of relay 116, left-hand winding of low resistance relay 117, right-handwinding of relay 11-1, tip ofjack 103, tip of plug 101. up perright-hand winding of repeating coil 112s of the operators cord circuittoground. .\t the insertion of the plug 101, a second circuit for rela'y114 is also established as follows; battery, winding of calledsupervisory relay 1.19, lower right-hand windin of repeating coil 118,ring of plu 101 and ring of jack 103, winding of trim connecting relay120. right-hand winding of relay 111, to grouml at the repeating coil118 as above traced. The resistance of this path. from battery to groundis so high as compared with the above tracedpath to ground through relay114 that the supervisor relay 119 and relay 120 do not receive su'cientcurrent to op crate. The stepping relay 114,? attracting itsarmature closes a bridgentiss the outgoing end of trunk 1011, 105 whichresults in the energization of the repeating relay 202 at the calledexchange. Fig. 2. The circuit of relay 202 may be traced from battery.

right-hand winding of such relay, contact 203.1101? trunk connectingrelay 201, trunk "conductor 105, outer left-hand armature and contact ofrelay 116, winding of a polarized relay 121, right-hand winding of relaylll',

armature ant contact of relay 114. inner lei't hand armature and backcontact of relay 110. trunk conductor 104-, contact 205 of relay 204,left-hand wincling of relay 202, upper right-hand winding of repeatingcoil 200 to ground. The direction of current in this circuit is such asnot to cause the energization of the polarized relay 121. Relay 202 atits front contact closes a circuit for slow relay 207, which in turnprepares a stepping circuit for the operating magnet 20b of the selectorswitch at the second exchange, and also places a break point in thecircuit of the release magnet 210 of such switch.

The operator, having obtained the number of the called line 300, 2301.of the dista t change, now presses her calling key 122 and manipulatesthe sending device. 123 to produce a series of short interruptions inthe circuit of stepping relay 111 determined by the first digit of suchnumber. f In response to these interruptions, relay 114 vibrates itsarmature. thereby producing a series of.interruptions in the abovetraced circuit of repeating relay 202, which latter relay retracts andattracts its armature correspondingly. At the first retraction of relay202, an impulse is sent over the following circuit to the primarystepping magnet 208: grounded armature and back contact of relay 202,inner armature and front contact of slow relay 207, left-hand armature:wl contact of relay 211, condu ctor 212, winding of slow relay 2 13,side-switch arm 211 (position 1), Winding of magnet 208 to battery.Magnet 208 operates to impart one rotary step to the switch shaft 215.The slow relay 213 also energizes and closes a circuit from ground, overits lower armature. side-switch arm 216 (position 1), to the escapemagnet 217. The escape magnet energizes preparatory to releasing theside switch into second position. For each succeeding impulse the magnet208 ives the shaft 215 a rotary step and final y brings said shaft torest, at the end of the impulses. with a set of brushes, such as 218.210. 220 in operative relation to a group of terminals. such as 221,222. 223, of trunks leading to switches having access to the calledline. At the end of this first set of impulses relay 202 holds itsarmature attracted and after an interval the slow relay 213 deenergizesto open the escape magnet circuit. Said escape magnet now energizes andpasses the side switch into position 2.

When the, side switch reaches position 2. the escape magnet 217 is againenergized over a circuit from battery, winding of such magnet, left-handarmature and contact of magnet 210, side-switch arm 216 (position2),,conduct'or 221, contact 225,-now closed, side-switch arm 226(position2), to ground. A circuit for the second ry steppin magnet 200is now closed from 11nd, Side-S i ch arm 227 (position 2), cont t andarmature of magnet 217, contact and rmature and \yinding' of magnet 209to batte Magnet 209 thereupon energizes and adv nces shaft 1 ,334,eos

' selector switch. Escape magnet 217 is there- Fill fore held energizedover the following path, ha ry, winding of such magnet, contact aleft-hand armature of ma'gnet'210, sideswitch arm 216 (position 2),conductor 224, test brush 220, to a grounded terminal such as 223.Magnet 209 continues to operate until the brushes 218, 219, 220 reach anidle trunk, at which time the escape magnet 21? eleenergizcs to escapethe side switch into third position.

The selector switch at the second exchange, Fig; 2, is now standing witha set of its brushes 218, 219, 220 in contact with the terminals of atrunk leading to a connector switch. indicated by the brushes 409, 410

and 411, having access to the called line 300,

301. in said second exchange. The connector 400", 410', 411' is in everyrespect similar to the (collector shown in full at the third exchange,Fig. L, and from this point on the description of the completion of thecall from the subscribers line 100 to subscribers line 300, 301 will begiven with reference to the connector circuits shown in Fig.- 4.

As the side-switch arm 228 of the selector goes to third position thefollowing circuitis established for a relay similar to relay 400, Fig.l, of the connector illustrated by brushes 400, 410', 4:11, at thesecond exchange: ground, arm 228 (position 3) brush 220. terminal 223.a. test conductor similar to conductor 10!, Fig. 4, right-hand armatureand back contact of release magnet 402, sideswitch arm 403 (position 1),winding of relay 4.00, to battery. Relay 100 energizes and prepares animpulse circuit for the counector inn-rating magnets 404 and 405, and atits left-hand armature said relay 400 also intcrposor a reak point inthe circuit of releasmmagnct 402. The apparatus is now in t ondition toreceive the second or tens series urimpulses. The operator accordinglyopcrates lxw sender 1163 to produce the desired iumlwr of interruptionsin the circuit of stepping relay l1-l at the calling exchange. For eachsuch interriunion the repeating rcl:\ 202 retracts and attracts itsarmature, and at the first retraction thereof a. circnitiis losed fcntheprimary stepping magnet .1041.

al lln cullHBCtOI switch. This circuit is traceable fpom the groundedarmature and back contact of relay 202, inner armature and contact ofrelay 207 left-hand armature and at the same and contact of relay 211,conductor 212, winding of slow relay 213, side-switch arm 214 (position3), brush 218, terminal 221, a trunk conductor similar to conductor 406,conductor 407, outer right-hand armature and contact of relay 400,side-switch arm 40S (position 1),:winding of magnet 404, to battery.Magnet 404' energizes and advances the connector brushes 400, 410' and411' one rotary step. At the same time the slow relay 213 energizes toclose a circuit as follows for the connector escape magnet 412 ground,upper armature and front contact of relay 213, side-switch arm 232'(position 3), brush 219, terminal 222, conductors 413 and 414,side-switch arm 415 (position 1), armature and contact of relay 410,-winding of escape magnet 412, to battery. Said es cape magnet energizespreparatory to advancing the connector slde switch into second position.For each succeeding vibration of the repeating relay 202 the connectorprimary magnet 4.01 operates to impart a rotary step to the brushes I09,410' and 111. At the termination of this set of im'. pulses said brushesare brought to rest in operative relation to a group of terminalscontaining the terminals 42$,42fi, 430' of the called subscriber-s line300, 301. RM. 202 now remains energized and after a r 1"; cient intervalthe slow relay 213 relear: n interrupt the circuit traced for escape magnet 412. Said escape magnet thereby do energizes to pass the side switchinto its sec ond position. Side-switch arm 403 engages its second.contact before breaking connec tion with its first contact, andtherefore the relay All) remains energized over its inner right-handarmature and contact, second position contact of arm 403, to thegrounded test wire 4101.

The operator now sends out the final or units series of impulses,causing as before, the vibration of the repeating relay 202. In responseto the first retraction of relay 202 an impulse is sent to the connectorsecondary magnet 405. The circuit for this magnet loads from thegrounded armature of relay 202, over the previously traced path toside-switch arm 408, now in position 2, and thence to magnet 405 andbattery. Relay 213 again energizes and'completcs a circuit for escapen'ragnct 412,- which loads as before described from ground, upperarmature of relay 213, to conductor 414. and from here by way ofside-switch arm .15 (position 2), to escape magnet 112 and battery.Magnet +12 energizes to subsequently escapcthe side switch to thirdposition. A parallel circuit to the one just traccd for magnet 412 isalso completed to energize the slow relay 110. At each impulse sent tomagnet :05 such magnet operates to more. the brushes 409, 410', 411 overthe terminals of the selected group and finally brings them to rest incontact with terminals 428, 420. 430 of the called line 300, 301. At theend of the units impulses magnet 412 deenergizes as before to advancethe connector side switch into third position.

Assume first that, when the brushes 409', 410' and 411 arrive on theterminals of the called line, such line is already engaged. In this casea non-selectable potential will be found on the test terminal .30. fullpotential having been removed or reduced in any well-known way in theevent the line is busy as a calling line. or having been reduced by acircuit leading to ground at. the left hand armature and coi'itact of atest relay 417 with side-switch arm 418 in third position, or to groundthrough the right-hand low re stancewinding of relay 417 with sides itcharm 418 in position 4 at. some other final. selector if the line is busyas a called line. In either case the test relay 417 of the switch showndoes not receive sufiicient current through its high resistance windingto energize. With the sideswitch magnet now standing in position 3. theenergizing cir cuits of relays 400 and 410 are opened. As soonthereafter as relay 410 releases its right-hand armature the relay r00becomes inert. thereby closing a circuit from battery. winding ofrelease ma net 402. let't-hand armature and contact of relay 400.primary off-normal contact 420. to ground.

Release magnet 402 attracts its armatures and releases the brushes 409,410', 411. and the side switch to normal position. As the Switch reachesits normal position. primary off-normal contact 420 is opened. whichhowever, does not occur until slightly after the closure of the normalcontact. 421. Hence the magnet 402 remains energized over the followingcircuit: battery, winding of magnet 402, left-hand arnmture of relay400'. normal contact 421, resistance 4:22. front con tact and right-handarmature of magnet 402, to the grounded third wire 401. When theconnector side switch reaches its first position a ath is closed fromthe secondary winding 0 busy tone transformer 423, contact and left-handarmature of magnet 402, side-switch arm 424 (position 1). condenser 425,side-switch arm 4:26 (position 1), to the trunk conductor 413 leadingback to the first selector.- In any well-known manner this busy tone isinductively transmitted back to the operatofis telephone set. Being thusinformed of the busy condition of the called line, the operator notifiesthe calling subscl'iber of such fact. and removes the plug- 101 fromjack 103. The relay 114 thereupon deenergizes and opens the bridgeacross trunk conductors 104, 105, causing the repeating relay 202 tobecome inert. The slow relay 20'? now deenergizes and closes thefollowing circuit for the first selector release magnet 210: battery,Winding of magnet 210, conductor 3 53. back contact and outer armatureof relay 20?. conductor 234. inner left-hand armature and back contactof re lay 235. primary oif-normal contact 230. to ground. Magnet 210thereupon operates to restore the selector and its associated sideswitch to normal. \Vhen brush '220 moves off the terminal 223. ground isremoved from wire 401 and the release magnet 402 retracts itsarinatures. At the calling exchange. the removal of plug 101 alsosevered the circuit of relay 107, which retracted its armaturcs tocil'ace the lamp 108. and to remove the busy condition from terminal109. All apparatus is now in its normal restored position.

If. however, the called line 300. 301 is idle at the time connection isextended thereto. full potential is present upon the test terminal 430;when the final selector side switch passes to third position the testrelay 417 is. therefore, energized over a circuit including its highresistance winding. lelay 417 at its right-hand armature closes acircuit as follows: battery, winding of escape magnet 412. contact andarmature of relay 415. side-switch arms 415 and 427 (position 3).right-hand armature and low resistance winding of relay 417 to ground.Relay 417 at its left-hand arn'iature shunts out the high resistancewinding. thus reducing the potential of test multiples 430 to make thecalled line non-sclectable to other switches. parallel circuit to theone just traced for magnet 412 is also completed for the slow relay 419as side-switch arm 427 goe to third position. Relay 400 at this timeremains energized to hold the release circuit open over a circuit frombattery, winding of such relay 400; its inner right hand armature andcontact, contact and right-hand armature of the slow relay 419, to thegrounded third conductor 401. The escape magnet 41: energizing in theabove traced circuit applies ringing current to the called line asfollows: ringing source 431. relay 416, inner armature and contact ofmagnet 412. sideswitch arm 432, brush 410', terminal 429', over the loopof line 301. 300, terminal 428, brush 40$), side-switch arm 493, toground at the outer armature of magnet 412. When the called partyresponds the relay 416 operates, being marginal, and opens the circuitof magnet 412,

which deenergizes and passes the side switch into position 4. In thisposition the relay 400 is maintained energized by a circuit leading overarm .403 to the grounded conductor 401. As side-switch arm 4'27 leavesposition 3, the circuit for relay 410 is broken, but being slow torelease. said relay holds its armatures for an interval subsequent tothe arrival of arm 420 in fourth position. This causes an impulse to bereverted to the first selector over the following circuit: groundedleft-hand armature and contact of Relay 237 closes relay 419,side-switch arm i213 (position 4), conductor 413, terminal 222. brush21%, sideswitch arm 232 (position 3), upper armature and back contact oirelay 213, inner lower armature and back contact of relay 238,, lowerright-lumd Winding of repeating coil 2%, Winding of relay 237, tobattery. the following circuit for the first selector escape magnet 21?:grounded armature and contact of relay 237, lower middle armature andcontact of relay 238, inner left-hand armature and back contact of relay239, side-switch arm 216 (position 3), inding of magnet 21?, to battery.The escape magnet energizes, and as soon thereafter as the slow relay41$) retracts its armatures to open the momentarily closed circuit ofrelay 237, said escape magnet again dccncrgizes to release the sideswitch to position 4. Upon the side-switch arms 232 and 239 reachingposition t, a circuit is closed for relay 237, traceable from battery,winding of said relay, lower right-hand winding of repeating coil 206,inner lower armature and back contact of relay 238, up per armature andback contact of relay 213, side-switch arm 232 (position 4), bruslf 219,terminal 222, conductor 413, side-switch arm 432 (position 4), brush410', terminal 129. over the loop of station 301, 300, terminal 428,brush 409', sideswitch arm 433, conductor :06, terminal 221., brush 218,side switch arm 239 (position upper right hand winding of coil 200 toground.

The relay 237 thus energizes in series with the called line, andoperates to close a circuit for the trunk connecting relay 204 at theincoming end of the inter office trunk circuit 104, 105. Such circuitleads from grounded armature and contact of relay 237, conductor 240,left-hand Winding of relay 211, Winding of relay 204, to battery. Relay204 by attracting its armatures serves to remove the connection of trunkconductors 104, 105 with the 'windings'of repeating relay 202. and toconnect said conductors directly tlk the left-hand portion of repeatingcoil 2 6. The source of current fed to conductors 10 1, 105 from 206 nowflows in the proper direction for encrgizin polarized relay 121. Relay121 according attracts its armature and closes a circuit -om battery,armature and front contact of relay 121. windings of relays 116 and 124to ground at the right-ban armature of relay 107. Relays 116 and 121energize and lockup over a circuit extending from battery. contact111'), right-hand armature of relay 1.16, windings of relays 116 and 121to ground at the right-hand armature of relay 107. By the attraction ofboth the armature of relay 121 and the righthand. armature of relay 116,the previously traced low resistance path from battery through thewindings oi relays 117 and 114 the repeating coil to ground at the upperrighthand winding of repeating coil 118 is now opened. his causes anincreased flow of current through the supervisory relay 110 and trunkconnecting relay 120 in the circuit hercinbcfore described. llelay 11$)energizes and closes a circuit for the called supervisory lamp 125,which is displayed to inform the operator that the called party hasresponded. Relay 120 by attracting its armatures electrically connectsthe trunk 101, 105 to the operators cord circuit. lVhen relay 202 wasdisconnected from conductors 101 and 105 by the relay 204:, the circuitfor relay 207 was at the same time opened. This relay being slow,however, does not dccncrgize until relay 24:1 has time :to operate toclose a holding circuit therefor. Premature release 0' the switches isthus prevented. The connection is now complete for conversation.

After conversation is finished, the called. subscriber by replacing hisreceiver opens the above traced circuit for relay 237. This relay inturn causes the rh-ilinergization of trunk connecting relay 201, whichdisconnects the truth. llll, 105 from repeating oil 205, and againconnects said trunk in series with the repeating relay 202. This resultsin a reversal of battery current through polarized relay 121.Consequently relay 121 becomes inert and closes at its armature and backContact a low resistance path from battery to ground as above traced inparallel with the circuit over which called supervisiory relay 119 is atthis time being energized. This short circuit around relays 120 and 119causes a sufficient reduction in current to permit theirdelinergization, the former opening the outgoing end of the trunk 104,105 and the latter relay serving to extinguish the lamp 125. Theoperator, thus being informed that conversation is finished, removes herplug 101 from the trunk jack 103. Restoration of the suite ing mechanismthereupon takes place as already described.

It will now be assumed that a subscriber at an automatic substation, assubstation 113 belonging to the first exchange desires to be connectedwith the line 300, 301. Upon the removal of the receiver at substation113, the calling line is connected in a wellknown manner, as by means ofa line switch, to a trunk leading to an idle selector switch whosebrushes are shown at 110. 111 and 112. The subscriber now operates hisdial 126 to position the selector brushes 110. of trunks, such asterminals 127, 128 and 109 of trunks 104, 105, leading to the distantexchange to which the called line belongs. The selector then proceeds toautomatically test the terminals 100 and in the Wellknownunanncr bringsits brushes 110, 111, 112 to rest in connection with the first idletrunk found. The following circuit is now closed for stepping relay lll:battery, contact ll?) of relay 116, left-hand winding of low resistancerelay 117, r rhblnu'id winding of relay 1H, contact I" terminal 127,brush 114). o\'cl' the route substation 113, brush Ill. terminal 128.winding of relay 130, contact 131. letthand winding of re lay-11.4, toground. Relay 130 closes an energizing circuit for the supervisory relay107, which completes a circuit for lamp 108. The operator is therebyinformed that the trunk 104, 105 is engaged and will not at tempt tomake connections with the same by means of her cord circuits. The stepping relay 114 attracts its armatnres and closes a bridge. includingpolarized relay 121, across the trunk conductors 104 and 105 to energizethe re ieating relay 202 at the called exchange. Ihis circuit isprecisely the same as that traced in connection with an operators call.the direction of current flow being such as not to affect the polarizedrelay 121.

B v manipulating his dial 126, the subscriber at substation 11; causesthe stepping relay 11 1 to vibrate its armature in a man ner similar tothat already described in connection with the operation of the operators calling device 123. At each such interruption of the calling line.the relay 130 retracts its armature. but relay 107 being slow on releasedoes not have time to decncrgize to eltace lamp 108. From this point onthe operation tit-stepping relay 114 under the control scribe! serves tobring about the operation of the first and final selectors at the calledexchange. As has been described. when the called patty responds and thetrunk connecting relay 204 is operated to telephonically connect theincoming end of trunk IO-l, 105 to the called line. a current reversalresults as before. and polarized relay 121 now becomes energized. RelayI21 completes the circuit at its armature from battery through windingsof relay 1111 and the trunk onnecting relay 124 to ground at theright-hand armature and front contact of relay 1.07. Relay 116 is lockedup as before described and connects the outgoing end of the trunkcircuit 104. 105 to the calling line. A complete through telephonicconnecti n is now e tablished From the calling line in the lil'stexchange to the called line in the second exchange and conversation maytake place.

it has thus been described how a subscriber belonging to one exchangemay ohtain connection with a subscriber at another exchange over aninter exchange trunk. In this case the inter exchange trunk performs thefunctions of a terminating trunk at the called exchange. serving toextend the call ing line to autmnatic switches therein. which switchesare then operated to complete the ot' the calling sub connection to thedesired line. It will now be explained in what manner the abovementioned trunk may be joined ,in tandem to a second mtcr exchange trunkot' the the subscriber exchange. Fig. 4. call the line of subs the opeinccts sa 104. 105 leading to For tl subscriber at ator's position andoutgoing from ge and leading to a third ns purpose it will beassubstation 100 id line to an outgoing trunk circuit The completion ofoperating lays 10tt'or rela need no been informed by the the secondexchange.

circuits for reand 114 at the calling exchange and y 202 at the secondexchange being identical with that hereinbetore described,

t be repeated.

connection. is wanted with a change 123 in accordance W In the samemanner as here.-

called n shown in Fig. l. aetu 1th the H umber.

The operator, having calling subscriber that line at the exates hersender rst digit of the inbet'ore described. the repeating relay 202 atthe second exchange,

armatm tra nsnn pulses to the primary in witch. The magnet 208 lector scrates t Fig. 0 in response to the ts a correspondi o rotate the shaft 2brings the same to rest with t 218. 219 of'llPl'lll 220 in operativemals such as tcrnnna of trunks outgoing from t ch a a ge In thisinstance th by shaft 215,

end of stands on the contact 246.

relay 21 to pass and leading to the t the 3 and csca pc 2. vibrates itssender 123 and ng number of imagnet 208 of the sethereby 0p- 9 15 andfinally I set of brushes relation to a group ls 243. an be second exlnrdexchange.

e group brush 24-"), carried has been rotated so that at the groupelecting movement it As soon now as magnet 217 deenergizes the sideswitch into second position. a circuit is estahhsl'icd as follows:ground.

8 (position 2). act 2+6. winding of relay 239. it) energizes and closesa group new circuit for itself from battery. winding of relay 23!).right-hand tact of such l'elil).

hand armature of relay 211.

207. to ground. said relay 20? at this time.

The escape ma operates as above described Qlil. 22(

group 0 220 enc trunk. the esca and :id\ sltion. tlon the the trunkcontrolling rel battery,

sect

ve t I over the ternun armature and iconback contact and right conductor234.

Front contact of relay being operated gnet 21? again and closes thennlary magnet he brushes 218.

alsof the selectedv f outgoing trunks. When test brush ounters 'ancesthe side switch As the following circuit is ays windings of relays aterminal 244 of an idle pe magnet 2 l7 deenergizes into third poarm 22?reaches third posicompleted from 238 and 24?: 247 and 238,

outer left-hand fillllttl'llle and front contact These relays operate toremove the repeatwinding of such magnet. contact and ing coil 206 fromtrunk circuit and at the same time lock upras follows independently ofside-sWitch arm battery, windings of relays 247 and 238, lowermost.armature and contact of relay 238. conductor234, to ground at the outerarmature and front contact of relay in position 3 of thesidc switch theescape magnet 217 is again energized over a circuit from battery,

lefthand armature of magnet 210, side-switch arm 216 (position 3), innerleft-hand arma' ture and front contact of relay 239. to ground. \Vhentrunk relay 247 is energized, it establishes a. circuit as follows forthe.

trunk closing relay 204-. lowermost ground- 7 ing of repeating relay edarmature of relay 247, conductor 240, lefthand winding of relay 211.winding of relay 204, to battery. Relay 204 operates to disconnectrepeating relay 202 and to close the incoming end of trunk 104, 105.Relay 211 also operates in series with relay 204, thereby opening thepreviously traced locking circuit of relay 239. This relay 239 nowdeenergizes to disrupt the above described circuit of escape magi-ct217, which magnet thereupon passes t e side switch into its fourthposition.

It will be noted that the circuit of relay 207 is opened when repeatingrelay 202 is disconnected from the trunk conductors 104, 105. The relay207 being slow, however, does not release before the selector sideswitch has reached fourth position, at which time a circuit is completedto energize the relay 241 to thereby close a new circuit tohold saidrelay 207 energized. This circuit may be traced from battery. at thecalled exchange, Fig.3, right-hand wind- 305, contact 306, over theconductor 307 of the trunk interconnecting the second and; thirdexchanges, contact 308 of relay 313, conductor 309, terminal 242, brush218, side-switch arm 239 (position 4), upper armature and front contactof relay 238, up en armature and front ccntact of relay 24 upperarmature and contact 203 of relay 204, trunk conductor 105, outerleft-hand armature. an contact of relay 116, winding of polarized relay121, right-hand winding of low resistance relay 117, armature andcontact of relay 114, inner lefit-hand armature and back contact ofrelay 116, trunk conductor 104, contact 205 and lower armature of relay204, winding of relay 241, inner lower armatures and front contacts ofrelays 247 and 238, upper armature andrback contact of relay 213,side-switch arm 232 (position 4) brush 219, terminal 243, conductor 310,lay 311, contact 312 of relay winding of re 313, winding of polarizedrelay 314, trunk side-switcharm 227, to ground;

of the operators conductor 315, contact 310 of relay 317,

left-hand winding of relay 303. upper righthand winding of repmitingcoil 318, to round. By this operation the stepping relay 202 at hesecond exchange is disconnected from the trunk circuit. and current isnowdelivered from the. repeating relay 305 at the called exchange overthe two conductors of the. trunk in series back through the. secondexchange to the first or calling exchange. It will be observed that thedirection of current flow through polarized relay 121 is still the same;and consequently this relay remains inert. Also the direction of flowthrough the polarized relay 314 at the intermediate exchange is such asnot to operate the same at this time. Belay 305 by energizing in theabove traced circuit closes at its arn'iature and front contact acircuit for the slow relay 319. The apparatus is now in condition toreceive the next series of impulses.

For the purpose of this description. the called exchange, illustrated bythe right hand portion of Fig. 3 and by Fig. 4, is assumed to be of suchcapacity as to warrant only the use of final or connector switches.Hence the incoming end of the trunk circuit at the called exchange leadsdirectly to a connector switch, such as that shown in Fig. 4. The nextmanipulation sender 123 serves. therefore, to control the stepping relay114 in accordance with the tens digit of the called number. The relay114 by vibrating its armature o crates to intermittently open and closet e above described circuit for repeating rela 305 at the calledexchange. \Vhen slow relay 319 is energized, it closes the followingcircuit for relay 400 at the connector: grounded left-hand and contactof relay 319. conductor 401, right-hand armature and back contact ofmagnet 402. sideswitch arm 403 (position 1), winding of relay 400, tobattery. Upon the first retraction of repeating relay 305. a circuit isnow closed as primary magnet 404: grounded and back contact of relay305. right-hand armature and contact of relay 319. winding of slow relay320, back contact and upper armature of relay 321. conductors 406 and407, outer right-hand armature and contact of relay 400, side-switch arm408 (position 1), winding of magnet 404*, to battery. the same timerelay 320 energizes and places a ground upon the conductor 413. whighresults in the energization of the connector escape magnet 412 in amanner already described. The primary magnet 404 operates in response tothe tens impulses to rotate the connector brushes 409, 410 and 411. intooperative relation to the group of line ternnnals containing thetermlnals 428, 429

armature armature follows for the The operator now actuates the sender;123 to produce the final operation of the stepping relay 305 inaccordance with the units digit. At each retraction of relay 2105 animpulse is sent to the conm-ctor secondary magnet 405 over the abovetraced circuit to the arm 408. now in second position. and thence tosaid magnet 105. The side switch went to second position Hlll)('(lllt?llt to the transmission of the tens series as was clearlyexplained hercinbet'mc. The secondary magnet r05 thus operates toadvance brushes 109. 110 and 411 over the selected group and intoengagement with terminals 12-. 42.) and 130 of the called line. It suchline is busy. release magnet 402 is operated to re store the connector.and the busy tone is applied to conductor llll as above explained. Theoperator hearing this busy tone informs the calling subscriber that thedesired line is busy. and removes plug 101 from trunk jack 103. Removalof plug caused the deenergization of relays 107 and Ill. Relay 114. byretracting. opens the bridge across trunk conductors 10-l. 10:"). whichin turn results in the dciincrgization ot' relays 305 and 241. Relay241. by releasing, causes the slow relay 207 to deenergize. A circuitfor the selector release magnet 210 is now closed from battery. Windingof such magnet, conductor 233. back contact and outer armature of relay207, conductor 23-1, inner letthand almature and back contact of relav235. primary ofl nornlal contact 230 to ground, Release magnet- 210thereupon opcrates to restore the selector and its asso' ciated sideswitch to normal. As soon as the selector and its ssociatcd s i deswitch reach their normal positions/groand is removed from conductor234. and trunk rclays 247 and 238 deiinergize. lclay 217. by retractingits armatures. opens the circuit of relays 211 and 20-1, which in turnpermit their armaturcs to drop back. Allapparatus is now in its normalrestored condition.

If, however, the called line 43 i is idle when the connector arrivesupon its terminals 42R. 12!). 430. test relay 417 operatc relay 41!)remains energized. and escape magnet 412 again energizes to applyringing current, all as was clearly explained hereinhefore. When thesubscriber at substation responds, ringing cutofl' relar 410 operatesand the escape magnet 412 ad vanccs the side switch to position Din-inthe period the slow relay 419 is retaining its armatlues after thushaving its-circuit opened. and after the side switch has reached fourth,position, a moinentary circuit is established as follows: ground.left-haud armature and contact of slow relay r19. side-switch arm 426(position 4), conductor 413. armature and back contact of relay 330.lower righthand winding of repeating coil 318, windiug ot' rclav 322. to

battery. Relay 322 closes a circuit from battery, winding of trunk relay317. upper winding of trunk relay 321 to ground at the armature of relay322. Relay 321 operates and establishes the following circuit to holdrelay 322 energized in series with the called line after the slow relay41!) at the connector deiinerg'izes: battery. winding of relay 322.lower right-hand winding of repeating coil 31%. back contact andarmature of relay 2120, conductor 413. arm +32 (position 4). brush r10.terminal 420. over the loop of substation t ll. terminal 128. brush 409.arm 133. conductor 100. upper armature and front contact of relay 321.upper right-hand winding of repeating coil 31%. to ground. Relay 317operates to connect repeatin coil 318 to the incoming trunk circuit andalso dis-- connects repeating relay 305 at contacts 306, 316. Batterycurrent is now fed from repeating coil 318 back over the trunk circuitto the calling exchange in the opposite direction to that supplied byrelays 202 and 305 during the switch operating period. Polarized relay121 now responds to such reversal of current and in the same manner ashereinbetore described. causes the display of lamp 125. and theoperation of the, trunk closing relay 120. Polarized relay 314 at theoutgoingend of the trunk in the intermediate exchange likewise res modsto this current reversal to close the ollowing circuit: battery.windings of trunk relays 323 and 313. contact and armature of relay 314,to ground. Relays 323 and 313 operate. to connect repeating coil 32! inthe trunk circuit. It will be observed thebattery at the lefthandportion of repeating coil has now been substituted by battery at therepeating coil 318. to supply talking current to the calling; exchange.The direction of current is main tained the same. however. so that relay121 remains actuated. complete talking conncction has thus beenestablished from a calling exchange. through an intermediate and to acalled exchange.

'hen the called party hangs up his receiver at the end of conversation.relay 322 deenergizes and releases relays 317 and 321. Relay 311' onfalling back causes a reversal of current through polarized relay 314,which in turn becomes inert and causes relays 3323 and 31;, to retract.Release of the relay 32-? reverses current through polarized relay 121.which retracts to cause the deencrgization ot' relays 110 and 120.Called supervisory lamp 125 is therefore efl'aced to inform the operatorthat conversation is completed. The operator removes the plug 101 whichetl'ccts a restoration of the switch ing apparatus.

It is thought that the manner in which an automatic line at the firstexchange may be extended intovconnection with a called line at the thirdexchange, is obvious from the foregoing description. Itis thereforeunnecessary to trace out such a call in detail.

(onsidering Fig. 5 there is shown a portion of the outgoing end of atrunk circuit arranged to extend calls originating in the secondexchange to the third-exchange. X suhscriher at an automatic substation(not shown) in the second exchange, Fig. 2. upon initiating a call tothe third exchange. Fig. 4. connects his line by means of line andselector switch s (not. shown) to the trunk conductors 500. 501. Acircuit is thereupon established from battery, armature and hack contactof polarized relay 502, left-hand winding of relay 503. right-handwinding of stepping relay 504, contact 505, conductor 500, back over theloop of the calling line (not shown) and thence returning by way ofconductor .301, winding of relay 506, con

' tact 507, to the left-hand winding of relay .third exchan ge beingresponsive pulses to turther extend said through trunk 5304 and ground.From here on the operation of the circuits shown in Fig. 5 issuhstantially identical to that given in cone nection with theestablishment of a call from the automatic substation 113. Fig. 1., to awanted line in a distant exchange.

In the disclosure of the present invention. the originating exchangeonly isshown as being arranged to accommodate both manual and automaticlines, and the third or called exchange is described as a satellite ofthe intermediate exchange. Yet it is to he understood that the inventionis not limited to this specific arrangement. In fact each exchange maybe provided with both classes of lines, and also with inter exchangetrunk c'ircuits such that a. calling line, whether manual or automatic,at any exchange in the system may he aflorded the above describedtrunking facilities with any other exchange in the system.

What is claimed is:

1. In a telephone system, a plurality of exchanges, a trunk circuitoutgoing from a first and terminating ina switch at a second of saidexchanges. a source of talking cur' rent in said trunk circuit, a lineterminating at the second exchange, a second trunk cil" cuit outgoingfrom the second exchange and terminating in a switch at a third of saidexchanges, means for sending impulses over the trunk from the first tothe second excharse, said switch at the second exchange being responsivethereto to connect said first trunk either to said line or to saidsecond trunk, and means operated by the cstahlish meut of such latterconnection to disahle source of current and to convert said trunks intoa single through trunk arranged to transmit impulses directly from thefirst to the third exchange. said switch a; the to uch im circuit.

.4. In a telephone system, a plurality of exchanges. a trunk circuitoutgoing from a first and terminating in a switch at a second of saidexchanges. a line. terminating in the second exchange, a source oftalking current in said trunk circuit for supplying said line, a secondtrunk circuit outgoing from the second and terminating in a switch at athird exchange. means [or sending impulses over the two conductors ofthe trunk in series from the first to the second exchange. said switchbeing responsive thereto to connect said first tit-ink either to saidline or to said second trunk, and means operated by the switch in theesL-ddislnncut of such latter connection to disahle 2 itllll'L'l. ofcurrent and to contert said trunk into a single through trunk arrangedto transmit impulses directly from the first to the third exchange overits two coinluctors in seriei, said switch at the third exchange hcingresponsive to such impulses to further extend said through trunk.

3. In a telephone system, a plurality of exchanges, a trunk circuit.outgoiu from a rst and terminating at a. second of said exchanges. aline terminating in the. second exchange, a battery in said trunk.circuit for supplying said line, a second trunk circuit outgoing fromthe second and terminating in a third exchange, means for sendingimpulses over the trunk from the first to the second exchange, meansresponsive thereto to connect said first trunk either to said line or tosaid second trunk. means operated'hy the establishment of such latterconnection to disconnect said batter) and to convert said. trunks into asingle through trunk circuit arranged to transmit impulses directly fromthe first to said third exchange. a called line. means at the thirdexchange responsive to such impulses tot-extending said thrt'iuglr trunkcircuit to the called line, a plurality of sources of talking currentassociated with said through trunk. circuit hut disconnected therefromduring the transmission o1 impulses, and means operated upon theresponse of the called subscriber for rendering said sutures of currentetl'cct re,

i. In a telephone system. a plurality of exchanges. a connecting circuitoutgoing from a first and terminating at a second of said exchanges. aline terminating in the. second exchange. a battery in said clmncctlugcircuit for supplying said line. a second connecting circuit outgoingfrom the second and terminating at a third exchange. means tor sendingimpulses over the connecting circuit from the first to the secondexchange. incans responsive thereto to connect said lir t connectingcircuit either to said line or to said second connecting circuit. meansopci'aicil hr 1hc establishment of such latter i'wiillt'tllljvll to diconnect said battery and to convert said connecting circuits into asingle.

at the second exchange. i

ill)

lllll through trunk circuit arranged to transmit impulses direct l vfrom the first to the third ibicliange, it called line, means at thethird ixchange responsive to such impulses for ex lending said trunkcircuit to the called line, a iplnrahty of sources oi 10 qt the calledsuhsi rihcr for rendering one of s itid sources .eti'ectivc, meansoperated for thereupon rciersing the current in said trunk circuit.and'meaus responsive to such current reversal for rendering; the otherof 1.3 said sources etl'ecliv'e.

5. in a telephone system. a plurality of exchanges, a connecting circuitoutgoing; from a first and terminating at a second of said exchanges,aseeontl connecting circuit 20 outgoing from the second and terminatingin a third exchange. means for sending inipulses over said firstconnectingcircuit to the second exchange, means responsive. thereto forconnecting said first circuit to 25 said second circuit, means operatedby the :50 exchange,

5 but lnetl'ect ire 40 over said trunk circuit and 4-3 exchanges. aconnecting fin pulses over 5:, converting said circuits in at) to thecalled line. a

connection for convertin said connecting circuits into a single throughtrnnli' circuit adapted to transmitimpulses directly from thedirst tothe thir l a called line. means at the third exchange responsive to suchimpulses for ell tending said trunk to said line. a source q'f talkingcurrent at said first and third civchanges associated with said trunkcircuit during the transmission of impulses means operated upon theresponse of the. called suhscriher for rendi' ringi effective saidsource at the third exchange, moans also operated to reverse the currentmeans responsive to such current reversal for rendering cft'ective saidsource of talking current at the, first exchange.

(3. In a telephone system.

establishment of such a plurality of circuit outgoing from a first andterminating at a second of said exchanges. a second connecting circuitoutgoing'i'roni the second and terminating at a third exchange. meansfor sending imthe connecting circuit i'roiii the first to the secondexchang means responsive thereto for coiniectine' said fir t circuit tosaid second circuit. means operated hy the estahlishmcnt of suchconnection for a single trunk ircuit adapted to transmit impulsedirectly t'romthe first to the third exchange. a called line means atthe third exchange responsive to such impulses to extend aid. trunli'circuit lillll'alii) ol ources of talking current a sociated \ruh saidil'llllk circuit incll'e t'irc dill'iug'thc transmission of impulses.means operated upon the response of the called suhscrihcr l'oi renderingone. of said si'iurccs eli'cctirc, such source serving p thetransmissidbpof Lin}:

to thereupon reverse. the current over said trunk circuit, and iolarizedrelays operated in response to such reversal of current to renderefl'ectivo the remaining of said sources of talkingcurrent,

7. In a telephone system, a calling line. a trunk circuitterminating ina switch, means for assoeiatiing said line with said trunk, a' secondtrunk circuit terminating in a switch, :1 called line, means asso iatedwith the calling line for sending impulses over said first trunk, saidfirst switclrheing responsire thereto to connectsaid first trunk to saidsecond trunk, means operated upon the establishment of such connectionfor converting said trunks into a single circuit ar ranged to transmitimpulses directly from said sending means to said second switch, saidsecond switch being responsire thereto to extend the connection to thecalled line a source of talking current for each of said trunks, meansoperated upon the response of the called subscriber for connecting oneof said sources to said second trunk, means for thereupon reversing thecurrent over said first trunk, and means responsive to such currentreversal for connecting the other source of currait to said first trunkfor conversation.

8. In a telephone system, a connecting circuit terminating in a switch,a second eonecting circuit teri'ninatin in a second svitch, an impulsedevice 'or sending impulses over the circuit leading to said firstswitch, said i ist switch being responsive to said impulses ..2 connectsaid first circuit to said second circuit, means operated by theestablishment of such connection to convert said circuits into a singletrunk cireuit adapted to transmit impulses directly from said impulsedevice to said second switch, a called line, said second switch beingresponsive to such impulses to extend said trunk circuit to the calledline, a plurality of sources of talking current associated with saidtrunk circuit but ineffective during; the transmission of impulses,meansoperated upon the response of the called subscriber for renderingetfectiveone of said sources of current, such SOUICBSQI'ViIlg tothereupon reverse the current over said trunk circuit, and meansresponsive to such reversal of ci'irrcnt for rendering etl'ective theremaining of said sources of talking current.

9. In a telephone system, an established connection from a calling -lineto a called line congprising a trunk circuit extending from a rstexchange tln-ou h a second to a third exchange, said truth circuit beingarranged to transmit. 'mpulses directlv from the first to the third e:ehange 'during the estahlislnnent of said connection, sources of talkingcurrent associated with said trunk circuit hut disconnected therefromduring means operllll ated upon the response of the called subrrillol'for connecting one of said sources to said trunk, such source serving toreverse the flow of current over said trunk. and means responsive tosuch reversal of current for connecting the other of said sources ofcurrent to said trunk circuit for conrcrsze tion.

10. In a telephone system. a plurality of exchanges. an operatorsposition in a first oi said exchanges, a supcrvisouv signal at saidposition. a connecting circuit outgoing from said first and terminatingat a second exchangea second connecting circuit outgoing from the secondand terminating in a third exchange, means for sending impulses from thefirst to the second exchange. means responsive thereto for connectingsaid first circuit to said second circuit, meansoperated by theestablishment of such connection for converting said circuits into asingle trunk circuit arranged to transmit impulses directly from thefirst to the third exchange, a called line, means at the third exchangeresponsive to such impulses to extend sald trunk circuit to the calledline, a source of talking current associated with saidtrurk circuitnormally disconnected therefrom during the transmission of impulses,means operated upon the response of the called subscriber or renderingsaid source of current effective. such source serviu to thereuponreverse the current over suit trunk circuit, and means responsiw to suchreversal of current for operating said supervisory signal.

In witness whereof, we havehereunto subscribed our names.

ALBEN E. LUNDELL. ARTHUR B. SPERRY.

